Sunday, March 17, 2013

2013 Cervelo RCa revealed

I was floored by what I've seen by the new Cervelo RCa, which was just announced. The thing comes closest to perfection in a diamond-shaped bike for it's geometry that I've seen.

A very brief digression: In the past, bikes are designed for fit and stiffness and mass. Aerodynamics was always a factor, but it was relegated to fit: for 100+ years riders have realized they could go faster if their backs were flatter. But all bikes were made out of the same 1-inch steel tubing, as this worked well.

That changed in the 1980's, when Klein came out with his Al frame. With Al, the tubing can be made thinner with the tube diameter larger to get improved stiffness at lower mass. Other companies, like Cannondale, picked up the same trend. This flaunted aerodynamics, since the fatter tube bikes have more wind drag. But the effect of the increase in wind drag was quantitatively hard to assess, while weight and stiffness are directly detectable, and riders kept winning races on the bikes so it was considered to be an acceptable trade-off.

Carbon fiber frames started in the 1970's, picked up steam in the 1990's, and came to dominate in the 2000's. With carbon, as with aluminum, fatter tubes could also be made stiffer and lighter. Aerodynamics again suffered.

Aerodynamics has recognized to be a factor in frame design since the 1980's, when wind tunnel tests first became popularly used in cycling, first on equipment, and later, on specific riders. Early bikes like the Trimble used unified frame structures, but the UCI (international cycling union) ruled that racing bikes had to be traditional diamond-shaped, more out of aesthetics than any rational basis. Kestrel was the first to come out with a real aero-optimized mass-start frame. Cervelo took the next leap forward with the SLC-SL. Others followed. Each of these bikes used airfoil-shaped tubes to some extent. These added a lot of mass, even though the SLC-SL came in at just under 1000 grams, still much lighter than today's not-so-aero Pinarello Dogma, for example. I always admired these bikes for their engineering but never found them attractive. Pro riders agreed, in part perhaps because they were always compromised on comfort and stiffness. The only such bikes which got widespread professional was the Cervelo SLC and SLC-SL. But even there some of their riders, including most notably Carlos Sastre who won the Tour de France, preferred their R-series "Squoval-tube" bikes, despite the engineering data which suggested he had no business winning that tour with the aerodynamic penalty, perhaps 2% total wind resistance, of those bikes.

Scott really broke the mold on aerodynamics with the Scott Foil (first called F1). They realized you could truncate the airfoil shape to the rear and still get much of the benefit. Before Scott, LiteSpeed had done something similar with their C-series, but in that case to allow integration of the water bottle into the aerodynamic profile on the downtube only. Scott applied it throughout the frame. The result was most of the aerodynamic benefit at much less mass cost, and ride feel could be better tuned since the tube profiles were closer to traditional. The Scott was a game-changer.

Other companies picked up on the model, perhaps the best example being Trek with its Madone-7. Trek's probably wishing now they'd dissociated themselves from the Armstrong reference in the bike name, but the bike was the first Trek in that series I thought was really well designed.

But there's a lot of copying and designing for appearance in the cycling industry, not so much real engineering-based optimization. Perhaps it's no coincidence that Trek did such a nice job on the Madone after hiring Damon Rinard, an engineer who first came into my attention when he published on-line instructions for how he built his own carbon fiber frame at home. Trek hired him, but he later moved to Cervelo.

It had long been the practice on bike companies to sell super-priced bikes to skim off the component of the market that viewed spending many thousands of dollars on a bike to be not just acceptable, but even preferable. The price threshold of these "limited" bikes started around $5k for the total bike, but as marketing people realized that even their preconceived notions of how much people with way too much money were willing to spend were low-ball, this price quickly accelerated. A few years ago Scott and Specialized blew through the $10k limit for a complete bike without pedals. But Cervelo has always focused on frame + fork, not total bike. And now they've cracked the $10k barrier with just that.

First it was the R-Ca, which was a gorgeous bike. But it was still firmly grounded in the Squoval tube shape of the R-series. Now they've broken into the truncated airfoil ground with their newly announced frame, the R-Ca.
The white paper is here. It describes some of the excellent engineering which went into optimizing the mass-versus-aerodynamic drag on the bike. Not described there is the ride characteristics. Cervelo has previously described how they integrate accelerometers over their test bikes to tune the stiffness versus comfort characteristics. They're wonderfully fact-driven. If something which looks aero, is considered by customers to be aero, but doesn't measure in the tunnel to be particularly aero adds mass, they leave it out. For example I don't see any "hidden brakes" on this bike, even though Cervelo was the first to patent brakes hidden in the fork (from what I know: Storck also did something similar).

So that was a long digression. The white paper is full of great stuff. For example, here's frame mass measurements for different model bikes. Despite the aerodynamic optimizations, you can see the RCa is super-impressive.

But this sort of plot isn't new. What's newer is companies actually providing the weight as a function of frame size, giving not just the best-case number, but the range of values expected due to manufacturing variation.

The curious thing about this is the trend. For the smaller sizes, the frame mass increases gradually with frame size. But then at 56 cm that changes. Presumably the longer tubes + the larger mass of taller riders (on average) suggested the need for fatter tubes. The weight thus increases rapidly from the strength-limited trend.

Suppose you were on the fence between 56 cm and 58 cm. The 58 cm bike appears to be designed with an increased emphasis on stiffness, while the 56 cm frame is designed more for optimal mass. I'm just conjecturing here, but if I was relatively light I'd then tend to go with the 56 cm frame. This is the advantage of custom carbon: you can design not only for size but also weight, power, and riding style. And for the price of this frame you can get close to two top-end custom carbon frames, for example from Crumpton. Still, these bikes won't be as finely optimized as the Cervelo. The small-time builders simply can't devote that much engineering into their designs.

So will I be on the list to buy one of these? No way. $10k is simply too much to spend on a race frame. But I deeply admire the engineering work. I'm not going to even try to compute a $/gram or $/watt number. People whose first response to this is the $ number are off-base. This bike is designed as the best-bike-which-Cervelo can build. Then they put a price on it. If people want to buy it, that's their business, just like it's their business if they want to buy an expensive sports car or piece of useless jewelry. I'm just glad Cervelo made it, because I am impressed, even if I don't much like the geometry with it's relatively slack seat tubes in the small sizes and it's exceptionally long head tubes.